In a mixing bowl, beat the brown sugar and butter together at medium speed until fluffy. Add the eggs and beat until combined. In a bowl, stir together the flour, baking soda, salt and cinnamon, then add to the butter mixture and combine. Stir in the chips by hand.
Drop the dough onto the prepared baking sheets by rounded 2-inch balls, leaving 2 inches between them. Bake for 10 minutes or until golden brown. Transfer to a wire rack to cool completely.
To make the filling: Combine the butter and shortening in a mixing bowl and beat with an electric mixer on low speed until smooth. Gradually add the confectioners’ sugar until combined then beat in the vanilla. Turn the mixer to high and beat until fluffy.
When the cookies are completely cook, spread the smooth sides of half the cookies with a heaping dollop of filling. Top each with a second cookie for the cookie sandwich. Makes a dozen cookies.